The present invention relates to methods and apparatus for determining the provenance of data carrying discs, such as compact discs (CD).
The CD is a read only storage medium. Originally, CDs were used for the storage of music and other audio data. However, formats, such as the CD-ROM format, have been developed facilitating the reliable storage of data for use by computers and other digital devices. The CD-ROM format has become very popular and has become the mass data storage medium for computer programs and other files.
CDs can store about 74 minutes of high quality stereo sound or about 650 megabytes of data or some combination of both. The value of a CD to the end user, because of the value of the data it stores, is typically much more than its physical cost. This has made it an attractive target for counterfeiters who can produce replicas of an original CD at a nominal cost and sell the replicas, at the market price for the data, to make large profits.
With distribution media such as audio tapes or video cassettes, the quality of counterfeit copies tends to be lower than that of the originals due to the corruption of the analogue signal in the copying process. There is no such degradation in the case of CDs, however, as all of the information is stored digitally. Counterfeiters can therefore produce counterfeit copies of CDs which are almost indistinguishable from original or bona fide CDs.
If it were possible to distinguish between an original or bona fide CD and a counterfeit, then the problems caused by counterfeiters could be substantially reduced. Law enforcement officials, for example, would have a means of identifying counterfeit CDs, and could more easily obtain search warrants and secure prosecutions. If a CD carries a program, that program could be used to check that it was loaded from a bona fide, original CD.
The present invention seeks to identify counterfeit CDs and other data carrying discs.
According to a first aspect of the present invention there is provided a method of determining the provenance of a data carrying disc, the method comprising the steps of determining physical characteristics of selected data recorded on a test disc, comparing the physical characteristics determined with the physical characteristics of the same data on a data carrying disc produced from a known source to determine whether the test disc has been produced from the known source.
The manufacturing process for a data carrying disc, such as a CD, begins with the production of a master, and in the physical manufacturing process of the master, variations are introduced which give the master distinctive physical characteristics and cause errors in the data. The master is used to form generations of discs, and the physical characteristics of the master are passed on, down the generations. A group of discs manufactured from the same source, therefore, consistenty exhibit the physical characteristics of the master, and those physical characteristics can be used as a xe2x80x9cfingerprintxe2x80x9d for, or identification of, that source.
This invention has relevance to all data carrying discs, such as CDs and DVDs (digital versatile discs) and other optical discs, where physical characteristics arising out of the physical manufacturing process, are consistently reproduced in all discs originating from the same source.
Thus, in a method of the invention, the physical characteristics determined arise from the physical manufacturing process and act as a fingerprint for a particular known source in the manufacturing process.
An embodiment of a method of the invention may be used to identify that a test is genuine when the physical characteristics determined from the test disc correlate with the physical characteristics of the same data from a known and genuine source. Similarly, the absence of correlation between the physical characteristics may be used to identify a counterfeit disc.
CDs carrying popular music or computer programs, for example, may originate from a number of masters from manufacturing plants in different countries. What is more, the or each master will not be used to directly form the CDs. Each master is used in the production of a number of stampers which are used to produce the discs sold in the marketplace. It will, therefore, be appreciated that although the fingerprint of one master will be apparent in its progeny, each stage of the process will also introduce fingerprints from the sources used in those stages.
The physical characteristics determined may be chosen as appropriate. In an embodiment, the physical characteristics determined are the locations of selected data on the disc.
For example, the physical characteristics may be the total length of the data carrying spiral track, or the radial positioning of specified sections of data. In one embodiment, the physical characteristics determined are angular orientations of specified sections of the data recorded on the disc. The angular orientations determined may be absolute or relative.
In a presently preferred embodiment, the specified sections of the data recorded on a data carrying disc from a known source lie substantially on a single radius of the disc.
The selected data whose physical characteristics are determined may be dedicated data sections. For example, the dedicated data sections may be introduced during manufacture along a radius of a master to provide copy protection for the discs made therefrom.
However, it is generally preferred to determine physical characteristics of selected, identifiable sections of the data on the disc as this enables the techniques described herein to be used to determine the provenance of existing discs.
In an embodiment, the selected data whose physical characteristics are determined are selected frames of the data recorded on the disc.
Preferably, the selected frames of data are at evenly spaced radial positions on a data carrying disc from a known source.
In an embodiment, the method further comprises the steps of extracting selected data from a test disc and determining the physical characteristics thereof, and at substantially the same time extracting the selected data from a disc from a known source and determining the physical characteristics thereof, whereby the comparing step is performed in real time.
For example, each of a test disc, whose provenance is to be determined, and a genuine disc from a known source are read in a respective disc reader and the determined information output from each reader is fed, for example, to processing means to enable the comparison to be undertaken.
Additionally and/or alternatively, the method may further comprise the steps of extracting selected data from a disc from a known source and determining the physical characteristics thereof, and recording the physical characteristics determined as a fingerprint of the known source.
There are different ways in which a method of the invention as defined above may be implemented. For example, measurements may be taken to determine the physical characteristics and to thereby enable the comparison. This would be an implementation in hardware.
Alternatively, data extracted from a disc can be processed to reveal information as to its location on the disc, for example, whereby physical characteristics thereof are determined. This would be an implementation in software.
Of course, an implementation which combines the two approaches would also be possible.
The present invention also extends to apparatus for determining the provenance of a data carrying disc by a method as defined above.
According to a further aspect of the present invention there is provided apparatus for enabling the provenance of a data carrying disc to be determined, said apparatus comprising means for determining physical characteristics of selected data recorded on a test disc, and means enabling the comparison of said physical characteristics determined with the physical characteristics of the same data on a data carrying disc produced from a known source.
Said means for enabling the comparison of physical characteristics may comprise a chart, table, graph or other hard copy representation of the physical characteristics of the selected data on a genuine disc. A similar representation of the physical characteristics determined for a test disc may then be displayed and/or printed and the comparison made by eye.
Preferably, however, said means enabling said comparison comprises processing means.
In one embodiment, said means for determining said physical characteristics of a test disc comprise means for rotating a test disc, sensor means for generating pulses representative of the angular orientation of the test disc, a pickup for extracting data from the rotating test disc, and circuit means for obtaining timing information from the extracted data.
It is possible to provide dedicated apparatus incorporating the features described above. However, it is generally preferred to modify a substantially conventional disc reader and a substantially conventional data extraction circuit to provide the data required for the comparison.
In the embodiments described above, the physical characteristics are determined by direct measurements. Additionally and/or alternatively it is possible to process the data on the disc to reveal information about the physical characteristics of the disc.
In a preferred embodiment, said means for determining said physical characteristics of a test disc comprise means for rotating a test disc, a pickup for extracting data from the rotating test disc, and circuit means for determining the location of the data extracted on the test disc.